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United States Department of Agriculture

Agricultural Research Service

Research Project: PROCESS-READY CUCUMBER PRESERVATION BY ACIDIFICATION WITH LESS THAN 2.4% ACETIC ACID

Location: Food Science Research

2012 Annual Report


1a.Objectives (from AD-416):
To evaluate a cucumber preservation method that would allow the processing of the preserved fruits without washes prior to packing into final product. The final cover brine formulation should preserve cucumbers for 9 months or more, and equilibrate with the fruits to contain about 1.1% acetic acid, reduced sodium chloride (4% or less), and pH 3.3 or lower.


1b.Approach (from AD-416):
ARS Scientists developed reduced sodium chloride and acetic acid cover brine formulations to effectively preserve cucumbers at pH 3.5 for up to a year in the absence of oxygen. It is the intent of this research to scale up the successful treatments from such laboratory trials to commercial products imported to the United States from India by Marcatus QED. Although the presence of oxygen in the commercial packaging is likely to encourage microbial growth and make the preservation more difficult to achieve, treatments containing 1.1% acetic acid, 0.45% calcium chloride, 0-4% sodium chloride, and combinations of either traditional preservatives such as potassium sorbate and sodium benzoate or natural preservatives, and fumaric acid will be tested. Phosphoric acid will be evaluated as an additional ingredient to achieve a pH of 3.3 or below, as the reduction of acetic acid to 1.1% will not make it possible to reach this target. Preliminary studies will be conducted concomitantly in North Carolina, USA and India with the aim of reducing the list of successful treatments, refine the cover brine formulations, and define the acidification needs for the preservation treatments to achieve a pH of 3.3. The evaluation of treatments in the United States would include the monitoring of microbial growth, primarily lactic acid bacteria, yeasts and molds, and enterobacteria, basic chemical analysis for sugars and organic acids, pH, titratable acidity and a single point texture evaluation. The evaluation of treatments in India will include the monitoring of the development of pressure and turbidity, and the determination of pH and titration of acidity. Treatments identified as effective during the preliminary stage will be further evaluated in Phase 1 and polished in Phase 2 to develop a close to commercialization formulations. The evaluation of treatments during Phases 1 and 2 will proceed in the same fashion described above for the Preliminary Trials in India.


3.Progress Report:

This project is related to in-house objective 2 targeting an increase in consumer acceptance of acidified vegetables that are refrigerated or preserved at ambient temperature without a thermal process by use of alternative acids and natural antimicrobial compounds to replace traditional preservatives, and by addition of pro-biotic lactic acid bacteria that provide health benefits to consumers.

Acidified cucumbers are imported in cover brine solutions containing 2.5 to 3.0% acetic acid, added as vinegar, and 4% sodium chloride, added as table salt. Preservatives such as sodium metabisulfite are also added to achieve preservation during transit, which may take up to 2 months. A significant portion of the processing cost is attributed to the addition of high concentrations of acetic acid and sodium chloride. Once in solution, sodium metabisulfite serves as the precursor for sulfite, which acts as the preservative or antimicrobial compound. It has been observed that sulfite concentrations in acidified cucumber cover brine solutions decrease during transit to the United States (US), indicating the presence of some sort of chemical reactivity. The reduction of sulfite concentrations during transit provides an opportunity for the proliferation of multiple yeast species in the imported goods, causing bloating of the cardboard containers upon arrival to the US and thus, rejection of the product and losses for the international producers.

Regulatory agencies in the US are implementing stricter standards for acidified cucumber processors. In particular, processors in the US are currently challenged with the reduction of chloride levels in the waste waters so that environmental pollution due to industrial activities is minimized. Thus, acquisition of acidified cucumbers containing high sodium chloride concentrations (4%) represents a problem considering that the local processing of such product generates millions of gallons of high chloride waste waters every year. The acetic acid content in the imported acidified cucumbers also generates a relatively high biological oxygen demand in the waste waters, translating into a need for a more robust water treatment system, which increases production costs.

A solution for the challenges associated with the importation of acidified cucumbers to the US includes the brining of the fresh fruits with 100 mM calcium chloride as opposed to 1M sodium chloride, 1% (150 mM) acetic acid instead of 2.5% to 3% and natural preservatives such as fumaric acid, plant derived extracts and lauric arginate at pH 3.5. ARS scientists showed that cover brine formulations containing 20 mM fumaric acid to inhibit the lactic acid bacteria and 2 mM allyl isothiocyanate or 3.8 mM cinnamaldehyde to control the yeasts population are effective at the laboratory scale. The sodium chloride free treatments have been effective against the natural microbiota from the fruits and inoculated acid resistant Lactobacillus plantarum and spoilage yeasts, such as Zygosaccharomyces globiformis and Z. bailii. Combinations of the plant derived extracts in reduced concentrations as compared to those listed above have been determined to exert a synergistic effect in achieving acidified cucumber preservation.

The evaluation of the proposed low acid and salt formulations at the commercial scale requires an integrated effort between researchers and local and international processors. ARS scientists have been collaborating with processors to test the low salt and acid treatments at a semi-commercial scale with successful outcomes. The second stage of this project will include the testing of selected treatments at the commercial scale in the International processing environment. This second stage will be initiated at the end of August 2012.


Last Modified: 4/17/2014
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